Aluminum sheet

ABSTRACT

This invention relates to an improved aluminum sheet material which, when integral color anodized, forms an anodic coating having a color from gold to black within a commercially acceptable thickness range. The alloy composition is essentially 0.05-0.20 percent silicon, 0.15-0.40 percent iron, 0.15-0.30 percent copper, 0.10-0.30 percent manganese, 0.6-1.0 percent magnesium, 0.04-0.12 percent chromium, and the balance aluminum and inconsequential amounts of other elements. In the process of forming the sheet product the alloy is cast into an ingot, homogenized at a temperature between about 1,000*F and 1,125*F and hot rolled to a desired thickness.

United States Patent [191 Dorward et a1.

.[ Feb. 19, 1974 1 ALUMINUM SHEET [73] Assignee: Kaiser Aluminum andChemical Corporation, Oakland, Calif.

22 Filed: Dec. 22,1911

[211 App]. No.: 211,063

[52] US. Cl 148/2, 75/139, 75/142, 75/147, 148/11.5, 204/58 [51] Int.Cl. C221 l/04, C22c 21/04 [58] Field of Search. 75/139, 142, 147; 148/2,11.5, 148/31.5, 12.7; 204/58; 72/364, 700

3,475,167 10/1969 Beatty et al 204/58 X OTHER PUBLICATIONS Alloy Digest,Al-42, August 1956.

Primary Examiner-Charles N. Lovell Attorney, Agent, or Firm-Paul E.Calrow; Edward J. Lynch [57] ABSTRACT This invention relates to animproved aluminum sheet material which, when integral color anodized,forms an anodic coating having a color from gold to black within acommercially acceptable thickness range. The alloy composition isessentially 0.05-0.20 percent silicon, 0.15-0.40 percent iron, 0.150.30percent copper, 0.10-0.30 percent manganese, 0.6-1.0 percent magnesium,0.04-0.12 percent chromium, and the balance aluminum and inconsequentialamounts of other elements. In the process of forming the sheet productthe alloy is cast into an ingot, homogenized at a temperature betweenabout 1,000F and 1,125F and hot rolled to a desired thickness.

5 Claims, No Drawings l ALUMINUM SHEET BACKGROUND OF THE INVENTION Thisinvention relates to an aluminum sheet material which, when anodized inan integral color anodizing electrolyte, will form an anodic coatinghaving a color ranging from a light gold to black within acommerciallyacceptable thickness range.

It is now well-known to integrally color anodize aluminum and aluminumalloy products, such as sheets, extrusions, castings and the like forarchitectural and other purposes where the integrally colored coatingprovides a high aesthetic appeal. The basic process was first describedby Deal et al. in U.S. Pat.'No. Re. 25,566 assigned to the presentassignee. The electrolyte described by Deal et al. is an aqueoussolution of sulfosalicylic acid and small amounts of sulfuric acidand/or metal sulfates included therewith. Subsequently, it has beenfound that many compounds, both organic and inorganic, can be utilizedwith small amounts of sulfuric acid and/or metal sulfates in aqueoussolutions to form integrally colored anodic oxide coatings. Examples ofthese compounds include sulfophthalic acid, sulforesorcinol,lignosulfophonic acid, oxalic acid, maleic acid, succinic acid, andcombinations thereof, and dichromates, molybdates, tungstates andvanadates. Many other compounds could be cited.

As used herein, the expression integral color anodizing and words ofsimilar import relate to the process of anodizing which forms a coloredanodic oxide coating characterized by a resistance which increases at asubstantial rate during the formation thereof and a color which isprimarily a function of the cell voltage during anodizing.

In the commercial color anodizing processes the desired color isnormally obtained by varying the electrical program employed duringanodizing, suchas current density, voltage and the like. The electricalprograms used heretofore have been (1) a two-stage program wherein theinitial stage is at a constant current density until a predeterminedpeak voltage is reached, and a second stage of constant voltage at thatpeak voltage until the desired color and coating thickness of obtained,and (2) a single-stage program wherein the current density is maintainedat a constant level until the desired color and oxide thickness isobtained. The current density in the constant current density stage mayrange from to 50 amp/ft and the voltage may range from 30 to 75 voltsinthe constant voltage stage. At times, the bath temperature is raised orlowered from a normal operating temperature of 25C to C and 35C fordarker and lighter colors, respectively.

During the initial development of the integral color anodizing processit became evident that, although the process would produce a largespectrum of colors on many aluminum alloys, the alloys employed forcommercial color anodizing would be quite limited. This was due to thefact that many aluminum alloys form mottled or streaked anodic oxidecoatings and, further, that many alloys could not be anodized to give abroad spectrum of colors without rather severely modifying anodizingparameters such as bath composition, bath temperature, current density,voltage, and the like. Changing of the bath composition and largechanges in bath temperatures are impractical and expensive procedures.Further, heretofore it has been extremely difficult to develop anodiccoatings within a commercially acceptable thickness range for exteriorarchitectural applications, ie. 0.5 to 1.5 mils, with a full range ofcolors by practical variations in voltage and current density and smallvariations, e.g. up to 10C, in bath temperature. The minimum thicknessfor anodic oxide coatings for use in exterior architectural applicationsset by the Aluminum Association is 0.7 mils. There is no limitation onthe maximum thickness for anodic oxide coatings, but from an economicstandpoint, the thinner the oxide coating the lower the cost involved inproducing the coating. Most anodic coatings for architectural coatingsvary from about 0.5 to 1.5 mils in thickness.

It was early found that different lots of the same alloy, when subjectedto the same anodizing program, would not produce oxide coatings whichwould match, ie. look the same when viewed side-by-side. The colordeveloped would be the same, e.g. gold, amber, statuary bronze or black,but there would be sufiicient differences in the shade or hue of thecolor that the anodized material would have a visually differentappearance and thus be commercially unacceptable. This variation in theshade or hue of the color was found to be due to a large extent to thevariations in composition and metallurgical structure which occur in theprocessing of the alloy.

E. C. Beatty et al., in U.S. Pat. No. 3,143,765, solved one aspect ofthis problem by developing an aluminum alloy for extrusions which woulddevelop a full range of colored anodic oxide coatings within acommercially acceptable thickness range, and which would form coloredcoatings which would match when color anodized in the same manner.

In the past, it has been necessary to provide at least two separatealloys, sometimes three, to obtain the full range of colors on sheetproducts. A modified 5005 alloy (Aluminum Association designation)described in U.S. Pat. No. 3,379,580, assigned to the present assignee,has been used to obtain colors from gold to dark brown or statuarybronze. A 5086 alloy (Aluminum Association designation) has been used toobtain a black anodic oxide coating. The popular dark brown, or statuarybronze, colored coating was extremely difficult to obtain with themodified 5005 alloy described in the above-mentioned patent, because ofthe long anodizing time and the large amount of total current quantitywhich was necessary to generate this color. For statuary bronzecoatings, typical anodizing times include up to an hour or more, andtypical total current quantities range up to 14 amp hrslft whichconsiderably increase the cost of the anodized product.

Against this background the present invention was developed.

DESCRIPTION OF THE INVENTION The present invention provides for a sheetproduct having substantially improved response to integral coloranodizing and a process for forming said sheet product. The product ischaracterized by a metallurgical structure which allows for theformation of an anodic oxide coating having a color ranging from lightgold to black within a commercially acceptable thickness range, ie. 0.5to 15 mils by changing anodizing parameters. Moreover, the sheet productwill consistently produce uniform coatings which will match when thematerial is color anodized in the same manner.

. 3 Essential to the present invention is an alloy compositionconsisting essentially of 0.05-0.20 percent silicon,

0.15-0.40 percent iron, 0.15-0.30 percent copper,

0.10-0.30 percent manganese, 0.6-1.0 percent magnesium and 0.04-0.12percent chromium, and the balance aluminum and inconsequential amountsof other elements. Preferably, the composition ranges from 0.08-0.14percent silicon, 0.15-0.25 percent iron, 0.16-0.25 percent copper,0.16-0.25 percent manganese, 0.70-0.90 percent magnesium, 0.04-0.08percent chromium, and the balance aluminum and inconsequential amountsof other elements. The sum of the copper and manganese contents shouldnot exceed 0.45 percent. The other elements should not exceed 0.05percent, preferably not more than 0.03 percent maximum each, and thetotal amount of other elements should not exceed 0.15 percent,preferably not more than 0.10 percent. Unless stated otherwise, allpercentages described herein are on a weight basis.

In accordance with the present invention, the above .alloy compositionis cast into ingot, normally by the direct chill casting technique,homogenized, and then hot rolled. If desired, the resultant product canbe cold rolled further. For consistent color reproducibility, the

homogenizing step must be conducted at a temperaturebetween 1 ,000-],125F for a period of time from 4-24 hours. Preferably, the maximumhomogenizing temperature variation from batch to batch should be i 30Fwithin the range of l,000-1,125 "F for more uniform color response. Arelatively slow heat-up rate of less than F/hr, particularly 75TF/hr,for homogenizing is preferred. After homogenizing, the ingots areallowed to cool to room temperature, preferably at a rate lower than100F/hr and then scalped. After scalping, the ingots are then reheatedto rolling temperatures, e.g. 750-8 50F and then hot rolled. An altemateprocedure after casting comprises scalping, homogenizing,

' 4 color of the resultant oxide coating, the chromium content of thepresent alloy is particularly critical for color reproducibility, ie.color match. Without chromium in the specified amounts, small variationsin the manga-' nese content, particularly in the lower portion of therange, create large variations in color when the workpiece is coloranodized in the same manner.

The following examples are given to further illustrate the advantages ofthe present invention.

Example I An ingot was DC cast having the following alloy composition:iron 0.21 percent, copper 0.18 percent, manganese 0.16 percent, chromium0.06 percent, silicon 0.13 percent, magnesium 0.73 percent, and thebalance aluminum with normal impurities. The ingot was homogenized at1,000F for 6 hours with a heat-up and cooling rate of 60F per hour,scalped and hot rolled at an initial temperature of 825F and a finaltemperature of 650F and'then cooled to room temperature. The specimenswere cleaned in an inhibited alkaline cleaner, deoxidized in a 50percent nitric acid solution, etched for 10 minutes in a percent causticsolution at 135F and desmutted in a 50 percent nitric acid solution.Four samples of this sheet material were anodized I in an aqueouselectrolyte containing 65 grams/liter sul- :TABLET Anodizing ParametersColor Current Peak Total Total Current Oxide Bath of Density 1 VoltageAnodizing Quantity Thickness Temp. Coating amps/ft Volts Time amp-hrs/ftmils C Gold 12 40 55 9 0.8 25

Amber 20 51 30 0.8 25

Statuary Bronze 30 65 I0 0.8

Black 65 12 i 0T9 1 5 cooling to hot rolling temperatures amines 'hotroll EXAMPLE ing. If desired, the sheet product can be cold rolled at atemperature below 250 F.

The above-described fabrication procedure in effect locks in thenecessary metallurgical structure to pro- Three separate alloys wereprepared, the composi- .tions of which are set forth in Table II, andthree ingots were cast from each alloy composition. One ingot from eachalloy composition was homogenized at temperatures of 1,000F, 1,075F and1,125F, respectively. The heat-up rate and cooling rate in each case was60F per hour. The ingots were then scalped at room temperature, reheatedto a temperature of 825F and hot rolled to a thickness of 0.14-inchthick. Samples of each of the resultant sheet products were thenprepared for anodizing by cleaning in an inhibited alkaline cleaner,deoxidizing in a 50 percent nitric acid solution, etching for 10 minutesin a 5 percent caustic solution at F, and desmutting in a 50 percentnitric acid solution for 1 minute. The samples were then anodized in anaqueous electrolyte containing 65 grams/liter sulfosalicylic acid, 5.8grams/liter sulfuric acid, and 1.7 grams/liter of dissolved aluminum.The temperature of the electrolyte was maintained at 25 C i 1C. Theanodizing program employed was a two-stage program in which the firststage was a constant current density of 30 amps/sq ft until a peakvoltage of 65 volts was reached, and the second stage was a constantvoltage period at 65 volts until a total current quantity of amp hrs/sqft had passed. The colors of all of the samples were a statuary bronzeand generally matched. The photometric color determinations are given inTable 11 below. The instrumental evaluation of the color was obtainedwith a Photovolt Model 610 reflectance meter with a Model T head. Thereflectance values were taken with reference to a porcelain enamelstandard calibrated against MgO at 100 percent. The yellowness factor isdetermined from the relationship Y= 100 (A B)/G where A is the amberreflectance, B is the blue reflectance and G is the green reflectance.

TABLE I1 Composition Allo Si Fe Mg Cu Mn Cr Al 1 .13 .21 .73 .18 .16 .06Bal 2 .10 .20 .75 .16 .24 .05 Bal 3 .12 .22 .84 .25 .19 .06 Ba] TABLEIII Instrumental Evaluation Allo Homo Green Yellowness No. Temp. ReflectFactor The green reflectance normally indicates the lightness ordarkness of the sample, the lower the reflectance value the darker thecolor. The yellowness factor generally indicates the yellowness of thesample; the higher the factor, the more yellow appearing in the coating.A green reflectance variation of less than 4, preferably less than 3,for lighter colors and less than 2.0, preferably less than 1, for darkercolors is generally acceptable for architectural applications. Asindicated by the above, the sheet products of the present invention arecharacterized by forming an integrally colored anodic oxide coatingwhich, when color anodized in a particular manner, has a color having agreen reflectance that varies less than 4 units, usually less than 3units, for lighter colors and less than 2 units, usually less than 1unit, for darker colors from another sample of said sheet material whichhas been anodized in the same manner.

It is obvious that various modifications can be made to the presentinvention without departing from the spirit of the invention or thescope of the appended claims.

What is claimed is:

l. The process of forming aluminum sheet material characterized by ametallurgical structure which allows for the formation of an anodicoxide coating between about 0.5 and 1.5 mils thick having a color fromlight gold to black when anodized in an integral color anodizingelectrolyte by varying anodizing parameters comprising preparing analuminum alloy consisting essentially of from 005-020 percent silicon,0.15-0.40 percent iron, 0.15-0.30 percent copper, 0.10-0.30 percentmanganese, 0.6-1.0 percent magnesium, 0.04-0.12 percent chromium, andthe balance aluminum and inconsequential amounts of other elements,casting said alloy into an ingot, heating said ingot at a rate of lessthan F/hr. to homogenizing temperature, homogenizing said ingot at atemperature of from about 1,000F to 1,125F for a period of time of aboutfour to 24 hours, and hot rolling said ingot to sheet gauge.

2. The method of claim 1 wherein the aluminum alloy consists essentiallyof 0.08-0.14 percent silicon, 0.15-0.25 percent iron, 0.16-0.25 percentcopper, 0.16-O.25 percent manganese, 0.70-0.90 percent magnesium,0.04-0.08 percent chromium, and the balance aluminum and inconsequentialamounts of other elements.

3. The method of claim 1 wherein the resultant sheet product is coldrolled at a temperature below 250F.

4. The preparation of aluminum sheet products by the method of claim 1from a plurality of ingots which have been homogenized in separate loadswherein the homogenization temperature from load to load does not varyby more than fl0 but in no instance is the homogenizing temperature lessthan 1,000F. or greater than 1,125F.

5. An aluminum sheet material formed by a. preparing an ingot of analuminum alloy consisting essentially of from 0.05-0.20 percent silicon,0. 15-040 percent iron, 0.15-0.30 percent copper, 0.100.30 percentmanganese, 06-10 percent magnesium, 0.04-0.12 percent chromium, and thebalance aluminum and inconsequential amounts of other elements; I

b. heating said ingot at a rate less than 100F/hr. to

homogenizing temperature;

c. homogenizing said ingot at a temperature from 1,000F. to 1,125F. fora period from 4-24 hours; and

d. hot rolling said ingot to sheet gauge, said sheet mate-rialcharacterized by metallurgical structure which allows for the formationof anodic oxide coating between 0.5 and 1.5 mils thick having a colorfrom light gold to black when anodized in an integral color anodizingelectrolyte.

UNITED STATES PATENT OFFICE RTIFICATE OF CORRECTION' Patent NO.3,793,089 Dated February 19, 1974 Inventor(s) a ph r Earl C?- Beatty,

and Jacquellne L. Thompson It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Frank L. Howard Page 1, Inventors, add the following:

Jacqueline L. Thompson, Spokane, Washington Signed and' sealed this 2ndday of July 1974.

(SEAL) Attest':

EDWARD M. FLETCHER,JR. C.M.ARSHALL DANN Attesting Officer Commissionerof Patents F ORM PO-1050 (10-59) USCOMM'DC 603764 69 U.Sr GOVERNMENTPRINTING OFFICE: ID! O-Jii-JJ,

2. The method of claim 1 wherein the aluminum alloy consists essentiallyof 0.08-0.14 percent silicon, 0.15-0.25 percent iron, 0.16-0.25 percentcopper, 0.16-0.25 percent manganese, 0.70-0.90 percent magnesium,0.04-0.08 percent chromium, and the balance aluminum and inconsequentialamounts of other elements.
 3. The method of claim 1 wherein theresultant sheet product is cold rolled at a temperature below 250*F. 4.The preparation of aluminum sheet products by the method of claim 1 froma plurality of ingots which have been homogenized in separate loadswherein the homogenization temperature from load to load does not varyby more than + or - 30* but in no instance is the homogenizingtemperature less than 1,000*F. or greater than 1,125*F.
 5. An aluminumsheet material formed by a. prepaRing an ingot of an aluminum alloyconsisting essentially of from 0.05-0.20 percent silicon, 0.15-0.40percent iron, 0.15-0.30 percent copper, 0.10-0.30 percent manganese,0.6-1.0 percent magnesium, 0.04-0.12 percent chromium, and the balancealuminum and inconsequential amounts of other elements; b. heating saidingot at a rate less than 100*F/hr. to homogenizing temperature; c.homogenizing said ingot at a temperature from 1,000*F. to 1, 125*F. fora period from 4-24 hours; and d. hot rolling said ingot to sheet gauge,said sheet material characterized by metallurgical structure whichallows for the formation of anodic oxide coating between 0.5 and 1.5mils thick having a color from light gold to black when anodized in anintegral color anodizing electrolyte.